In the production of circuit boards, connection of some components require relatively large areas of accurately measured volumes of solder. Commonly used mass-soldering application processes such as wave soldering are unable to provide the required solder volumes. Therefore, when large volumes are required to connect a component, flat preformed shapes of solder are positioned between the component and the circuit board, then the board, solder-preform and component are heated usually in an oven for reflow soldering the component to the board.
Individual solder-preforms are transported in bulk containers whether they are prefluxed or unfluxed, then they are removed from the bulk containers and positioned on a circuit board by hand or positioned in fixed trays for automatic application to the circuit board using a pick-and-place machine. Utilizing tubes and boxes for bulk distribution and dispensation are well-known. Robust flux coatings are available for the preforms which will not be damaged during bulk transportation. Alternatively, flux pastes and powders are available which can be applied to the preform or to the component and circuit- board during preform application or soldering. These fluxes are highly active so that. contamination is not a problem. After reflow, the flux is cleaned from the solder joint using solvents sufficiently mild to prevent damage to the circuit board.
Recently no-clean fluxes have become available which eliminate the need to clean the circuit board with solvent after reflow-soldering. The no-clean fluxes consist of a adipic acid or citric acid in a mild solvent such as water or an alcohol. The solution is applied to the components or to a solder preform and dried before soldering.
U.S. Pat. No. 3,351,192 to La Plate discloses a "package for cemented carbide inserts." U.S. Pat. No. 3,396,894 discloses an "applicator for simultaneously applying a plurality of bodies of solder. . . . When sheet 10 is transparent, the end of the heating cycle is easily observed." U.S. Pat. No. 4,209,893 to Dyce et al. discloses "A solder pack consists of a thin heat resistant carrier board having spaced holes therethrough in which are held solder rings." U.S. Pat. 4,354,629 discloses "solder material disposed between two polymeric layers, one of which is provided with window means to control the flow of solder."